diff --git a/CLAUDE.md b/CLAUDE.md
index 306bc29..c7ee102 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -35,6 +35,12 @@ Tiny Grid is a Python SDK for accessing electricity grid data from US Independen
 5. **Bulk Download Limit**: 1,000 documents per request
    - Archive bulk downloads limited to 1,000 files per POST request
 
+6. **RTC+B Changes**: December 4, 2024
+   - Real-Time Co-optimization + Batteries went live
+   - ESR (Energy Storage Resource) type added for batteries
+   - Real-time AS co-optimization replaces legacy ORDC
+   - All REST API endpoints remain compatible (additive changes only)
+
 ## Architecture
 
 The project follows a three-layer architecture:
diff --git a/README.md b/README.md
index aba6a67..890bf2e 100644
--- a/README.md
+++ b/README.md
@@ -296,6 +296,55 @@ Important limitations to be aware of:
 
 For data before December 2023, use `get_rtm_spp_historical()`, `get_dam_spp_historical()`, or the EIA integration.
 
+## RTC+B (Real-Time Co-optimization + Batteries) Support
+
+ERCOT launched RTC+B (Real-Time Co-optimization + Batteries) on December 4, 2024. This SDK fully supports both the new RTC+B changes and legacy endpoints:
+
+### What Changed with RTC+B
+
+| Change | Description |
+|--------|-------------|
+| **ESR Resource Type** | Energy Storage Resources (batteries) now participate in energy and AS markets |
+| **Real-Time AS Co-optimization** | Ancillary services are now procured in real-time alongside energy |
+| **New Price Signals** | RT SCED Price Adders, RT 15-min Price Adders replace legacy ORDC-based adders |
+| **ESR Data Fields** | New columns in disclosure reports for ESR capacity, awards, and state of charge |
+
+### Using RTC+B Data
+
+```python
+from tinygrid import ERCOT, ResourceType, AncillaryServiceType
+
+ercot = ERCOT(auth=auth)
+
+# Get ESR data from dashboard (no auth required)
+esr_data = ercot.get_energy_storage_resources()
+
+# Get ancillary service data (includes ESR participation)
+as_prices = ercot.get_as_prices(start="today")
+
+# Access resource type constants for filtering
+print(ResourceType.ESR)      # "ESR" - Energy Storage Resource
+print(ResourceType.GEN)      # "GEN" - Generation Resource
+print(ResourceType.CLR)      # "CLR" - Controllable Load Resource
+
+# Access ancillary service type constants
+print(AncillaryServiceType.REGUP)   # "REGUP" - Regulation Up
+print(AncillaryServiceType.ECRSM)   # "ECRSM" - ECRS Slow (10-minute)
+print(AncillaryServiceType.RRSFFR)  # "RRSFFR" - RRS Fast Frequency Response
+```
+
+### Legacy Endpoint Compatibility
+
+All existing REST API endpoints continue to work unchanged. The RTC+B changes are primarily:
+
+1. **Additive** - New data columns in existing endpoint responses
+2. **EWS Changes** - SOAP/XML web services have structural changes (not used by this SDK)
+3. **Deprecations** - SASM-related fields deprecated in EWS (legacy endpoints still work)
+
+**Key Dates:**
+- ESR Integration: June 1, 2024
+- RTC+B Go-Live: December 4, 2024
+
 ## Available ERCOT Endpoints
 
 Direct access to 100+ ERCOT endpoints organized by category:
@@ -315,7 +364,14 @@ All methods accept `**kwargs` for additional API parameters like `size`, `page`,
 ## Constants and Enums
 
 ```python
-from tinygrid.constants import Market, LocationType, LOAD_ZONES, TRADING_HUBS
+from tinygrid.constants import (
+    Market, 
+    LocationType, 
+    ResourceType,           # New: RTC+B resource types
+    AncillaryServiceType,   # New: AS types
+    LOAD_ZONES, 
+    TRADING_HUBS,
+)
 
 # Market types
 Market.REAL_TIME_SCED         # Real-time SCED (5-minute)
@@ -328,6 +384,20 @@ LocationType.TRADING_HUB      # Trading hubs (HB_*)
 LocationType.RESOURCE_NODE    # Resource nodes
 LocationType.ELECTRICAL_BUS   # Electrical buses
 
+# Resource types (includes RTC+B ESR)
+ResourceType.GEN              # Generation Resource
+ResourceType.ESR              # Energy Storage Resource (batteries)
+ResourceType.CLR              # Controllable Load Resource
+ResourceType.WGR              # Wind Generation Resource
+ResourceType.PVGR             # Solar (Photovoltaic) Generation Resource
+
+# Ancillary service types
+AncillaryServiceType.REGUP    # Regulation Up
+AncillaryServiceType.REGDN    # Regulation Down
+AncillaryServiceType.NSPIN    # Non-Spinning Reserve
+AncillaryServiceType.ECRSM    # Emergency Contingency Reserve - Slow
+AncillaryServiceType.RRSFFR   # Responsive Reserve - Fast Frequency Response
+
 # Pre-defined location lists
 LOAD_ZONES = ["LZ_HOUSTON", "LZ_NORTH", "LZ_SOUTH", "LZ_WEST", ...]
 TRADING_HUBS = ["HB_HOUSTON", "HB_NORTH", "HB_SOUTH", "HB_WEST", ...]
diff --git a/tests/test_constants.py b/tests/test_constants.py
index ce8576b..329c6be 100644
--- a/tests/test_constants.py
+++ b/tests/test_constants.py
@@ -5,13 +5,17 @@
     EMIL_IDS,
     ENDPOINT_MAPPINGS,
     ERCOT_TIMEZONE,
+    ESR_INTEGRATION_DATE,
     HISTORICAL_THRESHOLD_DAYS,
     LIVE_API_RETENTION,
     LOAD_ZONES,
     PUBLIC_API_BASE_URL,
+    RTC_B_LAUNCH_DATE,
     TRADING_HUBS,
+    AncillaryServiceType,
     LocationType,
     Market,
+    ResourceType,
     SettlementPointType,
 )
 
@@ -236,3 +240,111 @@ def test_column_mappings_values_are_strings(self):
         """Test that all column mapping values are strings."""
         for value in COLUMN_MAPPINGS.values():
             assert isinstance(value, str)
+
+
+class TestResourceTypeEnum:
+    """Test ResourceType enum (RTC+B).
+
+    RTC+B (Real-Time Co-optimization + Batteries) introduced ESR as a new
+    resource type for batteries in December 2024.
+    """
+
+    def test_resource_type_generation_values(self):
+        """Test generation resource type values."""
+        assert ResourceType.GEN == "GEN"
+        assert ResourceType.WGR == "WGR"
+        assert ResourceType.PVGR == "PVGR"
+        assert ResourceType.SMNE == "SMNE"
+
+    def test_resource_type_load_values(self):
+        """Test load resource type values."""
+        assert ResourceType.CLR == "CLR"
+        assert ResourceType.LR == "LR"
+        assert ResourceType.DSR == "DSR"
+
+    def test_resource_type_esr_values(self):
+        """Test ESR resource type values (RTC+B addition)."""
+        assert ResourceType.ESR == "ESR"
+        assert ResourceType.DESR == "DESR"
+        assert ResourceType.DGR == "DGR"
+
+    def test_resource_type_is_string(self):
+        """Test that ResourceType enum values are strings."""
+        assert isinstance(ResourceType.ESR, str)
+        assert isinstance(ResourceType.GEN, str)
+
+    def test_resource_type_str_representation(self):
+        """Test string representation of ResourceType enum."""
+        assert str(ResourceType.ESR) == "ESR"
+        assert str(ResourceType.GEN) == "GEN"
+
+
+class TestAncillaryServiceTypeEnum:
+    """Test AncillaryServiceType enum.
+
+    RTC+B modified how ancillary services are procured in real-time with
+    co-optimization of energy and AS.
+    """
+
+    def test_as_type_regulation_values(self):
+        """Test regulation service type values."""
+        assert AncillaryServiceType.REGUP == "REGUP"
+        assert AncillaryServiceType.REGDN == "REGDN"
+
+    def test_as_type_rrs_values(self):
+        """Test responsive reserve service type values."""
+        assert AncillaryServiceType.RRSPFR == "RRSPFR"
+        assert AncillaryServiceType.RRSFFR == "RRSFFR"
+        assert AncillaryServiceType.RRSUFR == "RRSUFR"
+
+    def test_as_type_nspin_values(self):
+        """Test non-spinning reserve type values."""
+        assert AncillaryServiceType.NSPIN == "NSPIN"
+        assert AncillaryServiceType.NSPNM == "NSPNM"
+        assert AncillaryServiceType.ONNS == "ONNS"
+        assert AncillaryServiceType.OFFNS == "OFFNS"
+
+    def test_as_type_ecrs_values(self):
+        """Test ECRS type values."""
+        assert AncillaryServiceType.ECRSM == "ECRSM"
+        assert AncillaryServiceType.ECRSS == "ECRSS"
+
+    def test_as_type_is_string(self):
+        """Test that AncillaryServiceType enum values are strings."""
+        assert isinstance(AncillaryServiceType.REGUP, str)
+        assert isinstance(AncillaryServiceType.NSPIN, str)
+
+    def test_as_type_str_representation(self):
+        """Test string representation of AncillaryServiceType enum."""
+        assert str(AncillaryServiceType.REGUP) == "REGUP"
+        assert str(AncillaryServiceType.ECRSM) == "ECRSM"
+
+
+class TestRTCBConstants:
+    """Test RTC+B (Real-Time Co-optimization + Batteries) constants."""
+
+    def test_rtc_b_launch_date(self):
+        """Test RTC+B launch date constant."""
+        assert RTC_B_LAUNCH_DATE == "2024-12-04"
+        assert isinstance(RTC_B_LAUNCH_DATE, str)
+
+    def test_esr_integration_date(self):
+        """Test ESR integration date constant."""
+        assert ESR_INTEGRATION_DATE == "2024-06-01"
+        assert isinstance(ESR_INTEGRATION_DATE, str)
+
+    def test_dates_are_valid_iso_format(self):
+        """Test that RTC+B dates are valid ISO format."""
+        import datetime
+
+        # Should not raise exception
+        datetime.date.fromisoformat(RTC_B_LAUNCH_DATE)
+        datetime.date.fromisoformat(ESR_INTEGRATION_DATE)
+
+    def test_esr_integration_before_rtc_b(self):
+        """Test that ESR integration date is before RTC+B launch."""
+        import datetime
+
+        esr_date = datetime.date.fromisoformat(ESR_INTEGRATION_DATE)
+        rtc_b_date = datetime.date.fromisoformat(RTC_B_LAUNCH_DATE)
+        assert esr_date < rtc_b_date
diff --git a/tinygrid/README.md b/tinygrid/README.md
index 780d665..5a7f0f3 100644
--- a/tinygrid/README.md
+++ b/tinygrid/README.md
@@ -223,10 +223,42 @@ Standalone data transformation functions:
 - `GridRateLimitError` - Rate limited (429)
 - `GridRetryExhaustedError` - Max retries exceeded
 
+## RTC+B Support
+
+The SDK supports ERCOT's RTC+B (Real-Time Co-optimization + Batteries) changes that went live in December 2024:
+
+### New Resource Types
+
+```python
+from tinygrid import ResourceType, AncillaryServiceType
+
+# ESR (Energy Storage Resource) for batteries
+ResourceType.ESR   # "ESR"
+ResourceType.DESR  # "DESR" - Distributed ESR
+ResourceType.DGR   # "DGR" - Distributed Generation Resource
+
+# All ancillary service types
+AncillaryServiceType.REGUP   # Regulation Up
+AncillaryServiceType.REGDN   # Regulation Down
+AncillaryServiceType.NSPIN   # Non-Spinning Reserve
+AncillaryServiceType.ECRSM   # ECRS Slow (10-minute)
+AncillaryServiceType.ECRSS   # ECRS Super Slow (30-minute)
+AncillaryServiceType.RRSFFR  # RRS Fast Frequency Response
+```
+
+### Key Dates
+
+- **ESR Integration**: June 1, 2024
+- **RTC+B Go-Live**: December 4, 2024
+
+### Legacy Compatibility
+
+All existing endpoints continue to work. The REST API paths remain unchanged - only the data within responses may include new ESR-related fields.
+
 ## Tests
 
 ```bash
 pytest tests/
 ```
 
-746 tests with 95% code coverage.
+821 tests with 96% code coverage.
diff --git a/tinygrid/__init__.py b/tinygrid/__init__.py
index fe39886..574bce0 100644
--- a/tinygrid/__init__.py
+++ b/tinygrid/__init__.py
@@ -1,7 +1,13 @@
 """Tiny Grid - A unified Python SDK for accessing grid data from all major US ISOs"""
 
 from .auth import ERCOTAuth, ERCOTAuthConfig
-from .constants import LocationType, Market, SettlementPointType
+from .constants import (
+    AncillaryServiceType,
+    LocationType,
+    Market,
+    ResourceType,
+    SettlementPointType,
+)
 from .ercot import ERCOT, ERCOTArchive
 from .errors import (
     GridAPIError,
@@ -20,20 +26,22 @@
 __all__ = (
     # Client
     "ERCOT",
+    # Constants/Enums
+    "AncillaryServiceType",
     # Historical
     "ERCOTArchive",
     # Auth
     "ERCOTAuth",
     "ERCOTAuthConfig",
+    # Errors
     "GridAPIError",
     "GridAuthenticationError",
-    # Errors
     "GridError",
     "GridRateLimitError",
     "GridRetryExhaustedError",
     "GridTimeoutError",
     "LocationType",
-    # Constants/Enums
     "Market",
+    "ResourceType",
     "SettlementPointType",
 )
diff --git a/tinygrid/constants/__init__.py b/tinygrid/constants/__init__.py
index ffef4ae..cfb7a21 100644
--- a/tinygrid/constants/__init__.py
+++ b/tinygrid/constants/__init__.py
@@ -3,23 +3,31 @@
 from .ercot import (
     COLUMN_MAPPINGS,
     ERCOT_TIMEZONE,
+    ESR_INTEGRATION_DATE,
     HISTORICAL_THRESHOLD_DAYS,
     LIVE_API_RETENTION,
     LOAD_ZONES,
+    RTC_B_LAUNCH_DATE,
     TRADING_HUBS,
+    AncillaryServiceType,
     LocationType,
     Market,
+    ResourceType,
     SettlementPointType,
 )
 
 __all__ = [
     "COLUMN_MAPPINGS",
     "ERCOT_TIMEZONE",
+    "ESR_INTEGRATION_DATE",
     "HISTORICAL_THRESHOLD_DAYS",
     "LIVE_API_RETENTION",
     "LOAD_ZONES",
+    "RTC_B_LAUNCH_DATE",
     "TRADING_HUBS",
+    "AncillaryServiceType",
     "LocationType",
     "Market",
+    "ResourceType",
     "SettlementPointType",
 ]
diff --git a/tinygrid/constants/ercot.py b/tinygrid/constants/ercot.py
index 83e2e6b..f9d2a9a 100644
--- a/tinygrid/constants/ercot.py
+++ b/tinygrid/constants/ercot.py
@@ -77,6 +77,43 @@ def __str__(self):
 # Rate limit (requests per minute)
 API_RATE_LIMIT = 30
 
+# ============================================================================
+# RTC+B (Real-Time Co-optimization + Batteries) Changes
+# ============================================================================
+#
+# RTC+B went live in December 2024 and includes:
+#
+# 1. ESR (Energy Storage Resource) Integration
+#    - Batteries can now participate in energy and AS markets
+#    - New resource type: ESR
+#    - Bidirectional dispatch (charge/discharge)
+#    - State of Charge (SOC) constraints
+#
+# 2. Real-Time AS Co-optimization
+#    - AS is now procured in real-time alongside energy
+#    - New price signals: RT SCED Price Adders, RT 15-min Price Adders
+#    - Replaced legacy ORDC-based price adders
+#
+# 3. New Data Fields
+#    - ESR-specific capacity and award columns in disclosure reports
+#    - New HDL/LDL fields for ESR base point adjustments
+#    - New MCPC fields for RT AS clearing prices
+#
+# Legacy Endpoint Support:
+# - All existing REST API endpoints continue to work
+# - Data returned may include new ESR-related columns
+# - SASM (Supplemental AS Market) fields deprecated in EWS
+#
+# For more information:
+# - ERCOT Technical Reference: https://www.ercot.com/mktrules/guides
+# - API Specs: https://github.com/ercot/api-specs
+
+# Date when RTC+B went live
+RTC_B_LAUNCH_DATE = "2024-12-04"
+
+# Date when ESR integration was enabled
+ESR_INTEGRATION_DATE = "2024-06-01"
+
 
 class Market(StrEnum):
     """ERCOT market types for price data."""
@@ -103,6 +140,58 @@ class SettlementPointType(StrEnum):
     RN = "RN"  # Resource Node
 
 
+class ResourceType(StrEnum):
+    """ERCOT resource types.
+
+    RTC+B (Real-Time Co-optimization + Batteries) introduced ESR as a new
+    resource type in December 2024. ESRs can provide both energy and
+    ancillary services with bidirectional dispatch (charge/discharge).
+    """
+
+    # Generation Resources
+    GEN = "GEN"  # Generation Resource
+    WGR = "WGR"  # Wind Generation Resource
+    PVGR = "PVGR"  # Photovoltaic (Solar) Generation Resource
+    SMNE = "SMNE"  # Small Non-Exempt Generation Resource
+
+    # Load Resources
+    CLR = "CLR"  # Controllable Load Resource
+    LR = "LR"  # Load Resource
+    DSR = "DSR"  # Demand Side Response Resource
+
+    # Energy Storage Resources (RTC+B)
+    ESR = "ESR"  # Energy Storage Resource (batteries, added in RTC+B)
+    DESR = "DESR"  # Distributed Energy Storage Resource
+    DGR = "DGR"  # Distributed Generation Resource
+
+
+class AncillaryServiceType(StrEnum):
+    """ERCOT Ancillary Service types.
+
+    RTC+B modified how these services are procured in real-time with
+    co-optimization of energy and AS. ESRs can now provide most AS types.
+    """
+
+    # Regulation Services
+    REGUP = "REGUP"  # Regulation Up
+    REGDN = "REGDN"  # Regulation Down
+
+    # Responsive Reserve Services (RRS)
+    RRSPFR = "RRSPFR"  # Responsive Reserve - Primary Frequency Response
+    RRSFFR = "RRSFFR"  # Responsive Reserve - Fast Frequency Response
+    RRSUFR = "RRSUFR"  # Responsive Reserve - Ultra-Fast Frequency Response
+
+    # Non-Spinning Reserve
+    NSPIN = "NSPIN"  # Non-Spinning Reserve (Online)
+    NSPNM = "NSPNM"  # Non-Spinning Reserve (Non-Market)
+    ONNS = "ONNS"  # Online Non-Spinning Reserve
+    OFFNS = "OFFNS"  # Offline Non-Spinning Reserve
+
+    # Emergency Contingency Reserve Service (ECRS)
+    ECRSM = "ECRSM"  # ECRS - Slow (10-minute)
+    ECRSS = "ECRSS"  # ECRS - Super Slow (30-minute)
+
+
 # ERCOT Load Zones
 LOAD_ZONES = [
     "LZ_HOUSTON",