docs: add guide for remaining LiteLLM work

Author: Aditya Puranik

LITELLM_REMAINING_WORK.md

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+# LiteLLM Integration - Remaining Work
+
+## Current Status
+
+**Completed**: LiteLLM provider works for **Agent blocks** in workflows.
+
+**Pending**: LiteLLM integration with **Copilot** (sim.ai's AI assistant).
+
+---
+
+## What's Done
+
+- LiteLLM provider implementation (`providers/litellm/`)
+- API route for model discovery (`/api/providers/litellm/models`)
+- Environment variables (`LITELLM_BASE_URL`, `LITELLM_API_KEY`)
+- Full tool execution and streaming support
+- Provider registered in store and registry
+
+---
+
+## Remaining: Copilot Integration
+
+The Copilot has a hardcoded model list separate from the provider system. To enable LiteLLM models in the Copilot, modify these files:
+
+### 1. Add LiteLLM to valid provider IDs
+
+**File**: `apps/sim/lib/copilot/config.ts`
+
+Add `'litellm'` to `VALID_PROVIDER_IDS`:
+
+```typescript
+const VALID_PROVIDER_IDS = [
+  'openai',
+  'azure-openai',
+  'anthropic',
+  'google',
+  'deepseek',
+  'xai',
+  'cerebras',
+  'mistral',
+  'groq',
+  'ollama',
+  'litellm',  // ADD THIS
+] as const
+```
+
+### 2. Update Copilot model options (Frontend)
+
+**File**: `apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/copilot/components/user-input/constants.ts`
+
+Option A - Add static LiteLLM entry:
+```typescript
+export const MODEL_OPTIONS = [
+  // ... existing options
+  { value: 'litellm/default', label: 'LiteLLM', provider: 'litellm' },
+]
+```
+
+Option B - Make model list dynamic by fetching from provider store.
+
+### 3. Update API validation schema
+
+**File**: `apps/sim/app/api/copilot/chat/route.ts`
+
+Update `ChatMessageSchema` to accept LiteLLM models. Find the `model` field validation and either:
+
+- Add a regex pattern for `litellm/*` models
+- Or dynamically validate against available provider models
+
+### 4. Update Copilot state types
+
+**File**: `apps/sim/stores/panel/copilot/types.ts`
+
+Update the `selectedModel` type in `CopilotState` to include LiteLLM model pattern:
+
+```typescript
+selectedModel: 'claude-4.5-opus' | 'claude-4.5-sonnet' | /* ... */ | `litellm/${string}`
+```
+
+---
+
+## Testing Checklist
+
+After implementing Copilot integration:
+
+- [ ] LiteLLM models appear in Copilot model selector
+- [ ] Can select and use LiteLLM model in Copilot chat
+- [ ] Streaming works in Copilot with LiteLLM
+- [ ] Run `bun run lint && bun run type-check`
+
+---
+
+## Submitting the PR
+
+### 1. Push to your fork
+
+```bash
+git push origin feat/litellm-provider
+```
+
+### 2. Create Pull Request
+
+Go to: https://github.com/simstudioai/sim/compare
+
+- Click "compare across forks"
+- Base repository: `simstudioai/sim`
+- Base branch: `staging` (NOT `main`)
+- Head repository: `adityapuranik99/sim`
+- Compare branch: `feat/litellm-provider`
+
+### 3. PR Template
+
+**Title**: `feat(providers): add LiteLLM provider integration`
+
+**Body**:
+```markdown
+## Summary
+- Add LiteLLM as a new provider for Sim
+- Enables connecting LiteLLM proxy to access 100+ LLM providers (including GitHub Copilot)
+- Uses OpenAI-compatible API pattern
+
+## Changes
+- New provider: `apps/sim/providers/litellm/`
+- New API route: `apps/sim/app/api/providers/litellm/models/`
+- Environment variables: `LITELLM_BASE_URL`, `LITELLM_API_KEY`
+
+## Test plan
+- [ ] Set `LITELLM_BASE_URL` in .env
+- [ ] Verify models appear with `litellm/` prefix in Agent block
+- [ ] Test chat completion through Agent block
+- [ ] Verify streaming works
+- [ ] Run `bun run lint && bun run type-check`
+
+## Note
+This PR enables LiteLLM for Agent blocks. Copilot integration can be added in a follow-up PR.
+```
+
+---
+
+## Environment Setup
+
+To test LiteLLM locally, add to `apps/sim/.env`:
+
+```bash
+LITELLM_BASE_URL=http://localhost:4000
+LITELLM_API_KEY=sk-your-key  # optional
+```
+
+Start LiteLLM proxy:
+```bash
+pip install 'litellm[proxy]'
+litellm --model gpt-4o --port 4000
+```
+
+---
+
+## Questions?
+
+- Discord: https://discord.gg/Hr4UWYEcTT
+- GitHub Issues: https://github.com/simstudioai/sim/issues