Litelm: LiteLLM Without the Bloat

litelm litellm's routing + translation in ~2,900 lines and 2 dependencies (openai, httpx). litellm routes LLM calls across providers and translates between message formats. That core is buried under 100k+ LOC of proxy servers, caching layers, cost tracking, and dozens of features most users never touch. litelm extracts just the call path — model routing, message translation, streaming, tool use, embeddings — and nothing else. No Router class, no proxy, no caching. Install pip install litelm # openai + httpx pip install litelm[anthropic] # + anthropic SDK pip install litelm[bedrock] # + boto3 pip install litelm[all] # everything Usage import litelm # Basic completion response = litelm.completion("openai/gpt-4o", messages=[{"role": "user", "content": "Hello!"}]) print(response.choices[0].message.content) # Streaming for chunk in litelm.completion("groq/llama-3.1-70b-versatile", messages=[...], stream=True): print(chunk.choices[0].delta.content or "", end="") # Embeddings response = litelm.embedding("openai/text-embedding-3-small", input=["hello world"]) Every function has an async variant: acompletion, aembedding, aresponses, atext_completion. The API mirrors litellm — same function names, same arguments, same response types. If you're using litellm today, switching is s/litellm/litelm/ in your imports. What's in / what's out Providers Routes to 19 providers via "provider/model-name" syntax. Any OpenAI-compatible endpoint works via api_base. API Keys Set the environment variable for your provider: export OPENAI_API_KEY=sk-... export ANTHROPIC_API_KEY=sk-ant-... Or pass directly: litelm.completion("openai/gpt-4o", messages=[...], api_key="sk-...") litelm.completion("openai/gpt-4o", messages=[...], api_base="http://localhost:8000/v1") Error Handling All provider errors are mapped to litelm's exception hierarchy: from litelm import ContextWindowExceededError, RateLimitError, AuthenticationError try: response = litelm.completion("openai/gpt-4o", messages=messages) except ContextWindowExceededError: # prompt too long — truncate and retry pass except RateLimitError: # back off pass except AuthenticationError: # bad API key pass Tool Calling tools = [{"type": "function", "function": { "name": "get_weather", "parameters": {"type": "object", "properties": {"city": {"type": "string"}}}, }}] response = litelm.completion( "openai/gpt-4o", messages=[{"role": "user", "content": "Weather in Paris?"}], tools=tools, tool_choice="required", ) tool_call = response.choices[0].message.tool_calls[0] print(tool_call.function.name, tool_call.function.arguments) Custom / Local Providers Any OpenAI-compatible server works via api_base: # vLLM litelm.completion("openai/my-model", messages=[...], api_base="http://localhost:8000/v1") # Ollama litelm.completion("ollama/llama3", messages=[...], api_base="http://localhost:11434/v1") # LM Studio litelm.completion("openai/local-model", messages=[...], api_base="http://localhost:1234/v1") Development transparency litelm is human-directed, AI-assisted software. Much of the code was written with Claude Code using Claude Opus 4.6/4.7. Code written from 2026-05-14 onward is written through Pi using GPT-5.5. Compatibility claims are based on tests and maintainer review, not AI authorship. Upstream attestation Maintainer attestation, 2026-09-11: LiteLLM's routing/formatting changes were reviewed from 649eb2d through 9a715df2. The audit triaged 360 core-path commits, inspected upstream tests for potentially relevant behavior, and fixed the resulting compatibility gaps test-first. Local scoped tests: 262 passed, 55 skipped; all 45 available-provider live tests and all 10 DSPy smoke tests also passed with the current dependency lock. This attests litelm's declared routing/formatting/DSPy surface only, not full litellm compatibility. Status Alpha. 262 own tests passing. The current scoped LiteLLM 9a715df2 baseline has 75 passing ported tests and no remaining actionable assertion/runtime failures. DSPy drop-in verified — all 7 execution paths proven live (Predict, CoT, typed signatures, streaming, embeddings, tool use, multi-output). Tests uv run --extra all pytest tests/ -x --ignore=tests/ported --timeout=10 # 262 non-live tests bash scripts/ported_contract.sh # 49 fast upstream contract tests uv run --extra all pytest tests/test_live.py -m live --timeout=30 # 45 live provider tests uv run pytest tests/test_dspy_smoke.py -m live --timeout=60 # 10 DSPy integration tests Live tests require API keys in .env.test. Skipped by default; run with -m live.