Add Anthropic Citation API support

[TomeHirata]

Add support for Anthropic Citation API through new types (dspy.Document, dspy.Citation). The design strategy is the same as dspy.Tool & dspy.ToolCalls.

Example

import dspy
from dspy.signatures import Signature

class AnswerWithSources(Signature):
    '''Answer questions using provided documents with citations.'''
    documents: list[dspy.Document] = dspy.InputField()
    question: str = dspy.InputField()
    answer: str = dspy.OutputField()
    citations: dspy.Citations = dspy.OutputField()

# Create documents to provide as sources
docs = [
    dspy.Document(
        data="The Earth orbits the Sun in an elliptical path.",
        title="Basic Astronomy Facts"
    ),
    dspy.Document(
        data="Water boils at 100°C at standard atmospheric pressure.",
        title="Physics Fundamentals",
    )
]

# Use with a model that supports citations like Claude
lm = dspy.LM("anthropic/claude-opus-4-1-20250805")
predictor = dspy.Predict(AnswerWithSources, lm=lm)
result = predictor(documents=docs, question="What temperature does water boil?")

for citation in result.citations.citations:
    print(citation.format())

References

• https://docs.anthropic.com/en/docs/build-with-claude/citations
• https://docs.litellm.ai/docs/providers/anthropic#beta-citations-api

[Copilot]

Pull Request Overview

This PR adds support for Anthropic's Citation API through two new types: dspy.Document for providing source content to language models and dspy.Citations for handling citation responses. The implementation enables citation-enabled responses from models like Claude, allowing developers to track which parts of the generated text reference specific source documents.

Key changes:

• Added Document type for representing citable source content with metadata
• Added Citations type for handling citation responses with character-level location information
• Integrated citation extraction into the base language model processing pipeline

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
dspy/adapters/types/document.py	New Document type with content, title, and metadata fields for citation-enabled content
dspy/adapters/types/citation.py	New Citations type with nested Citation class for handling citation responses
dspy/clients/base_lm.py	Added citation extraction from LiteLLM provider-specific fields
dspy/adapters/base.py	Integrated citation processing into adapter postprocessing pipeline
dspy/adapters/__init__.py	Exported new Citation and Document types
dspy/__init__.py	Made Citation and Document types available at package level
tests/adapters/test_document.py	Comprehensive tests for Document type validation and formatting
tests/adapters/test_citation.py	Tests for Citation types, extraction, and adapter integration

Comments suppressed due to low confidence (1)

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