OpenAI Assistants API v2

Status: Production Ready (⚠️ Deprecated - Sunset August 26, 2026) Package: openai@6.16.0 Last Updated: 2026-01-21 v1 Deprecated: December 18, 2024 v2 Sunset: August 26, 2026 (migrate to Responses API)

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⚠️ Deprecation Notice

OpenAI is deprecating Assistants API in favor of Responses API.

Timeline: v1 deprecated Dec 18, 2024 | v2 sunset August 26, 2026

Use this skill if: Maintaining legacy apps or migrating existing code (12-18 month window) Don't use if: Starting new projects (use openai-responses skill instead)

Migration: See references/migration-to-responses.md

---

Quick Start

npm install openai@6.16.0

import OpenAI from 'openai';

const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });

// 1. Create assistant
const assistant = await openai.beta.assistants.create({
  name: "Math Tutor",
  instructions: "You are a math tutor. Use code interpreter for calculations.",
  tools: [{ type: "code_interpreter" }],
  model: "gpt-5",
});

// 2. Create thread
const thread = await openai.beta.threads.create();

// 3. Add message
await openai.beta.threads.messages.create(thread.id, {
  role: "user",
  content: "Solve: 3x + 11 = 14",
});

// 4. Run assistant
const run = await openai.beta.threads.runs.create(thread.id, {
  assistant_id: assistant.id,
});

// 5. Poll for completion
let status = await openai.beta.threads.runs.retrieve(thread.id, run.id);
while (status.status !== 'completed') {
  await new Promise(r => setTimeout(r, 1000));
  status = await openai.beta.threads.runs.retrieve(thread.id, run.id);
}

// 6. Get response
const messages = await openai.beta.threads.messages.list(thread.id);
console.log(messages.data[0].content[0].text.value);

---

Core Concepts

Four Main Objects:

1. Assistants: Configured AI with instructions (max 256k chars in v2, was 32k in v1), model, tools, metadata
2. Threads: Conversation containers with persistent message history (max 100k messages)
3. Messages: User/assistant messages with optional file attachments
4. Runs: Async execution with states (queued, in_progress, requires_action, completed, failed, expired)

---

Key API Patterns

Assistants

const assistant = await openai.beta.assistants.create({
  model: "gpt-5",
  instructions: "System prompt (max 256k chars in v2)",
  tools: [{ type: "code_interpreter" }, { type: "file_search" }],
  tool_resources: { file_search: { vector_store_ids: ["vs_123"] } },
});

Key Limits: 256k instruction chars (v2), 128 tools max, 16 metadata pairs

Threads & Messages

// Create thread with messages
const thread = await openai.beta.threads.create({
  messages: [{ role: "user", content: "Hello" }],
});

// Add message with attachments
await openai.beta.threads.messages.create(thread.id, {
  role: "user",
  content: "Analyze this",
  attachments: [{ file_id: "file_123", tools: [{ type: "code_interpreter" }] }],
});

// List messages
const msgs = await openai.beta.threads.messages.list(thread.id);

Key Limits: 100k messages per thread

---

Runs

// Create run with optional overrides
const run = await openai.beta.threads.runs.create(thread.id, {
  assistant_id: "asst_123",
  additional_messages: [{ role: "user", content: "Question" }],
  max_prompt_tokens: 1000,
  max_completion_tokens: 500,
});

// Poll until complete
let status = await openai.beta.threads.runs.retrieve(thread.id, run.id);
while (['queued', 'in_progress'].includes(status.status)) {
  await new Promise(r => setTimeout(r, 1000));
  status = await openai.beta.threads.runs.retrieve(thread.id, run.id);
}

Run States: queued → in_progress → requires_action (function calling) / completed / failed / cancelled / expired (10 min max)

---

Streaming

const stream = await openai.beta.threads.runs.stream(thread.id, { assistant_id });

for await (const event of stream) {
  if (event.event === 'thread.message.delta') {
    process.stdout.write(event.data.delta.content?.[0]?.text?.value || '');
  }
}

Key Events: thread.run.created, thread.message.delta (streaming content), thread.run.step.delta (tool progress), thread.run.completed, thread.run.requires_action (function calling)

---

Tools

Code Interpreter

Runs Python code in sandbox. Generates charts, processes files (CSV, JSON, PDF, images). Max 512MB per file.

// Attach file to message
attachments: [{ file_id: "file_123", tools: [{ type: "code_interpreter" }] }]

// Access generated files
for (const content of message.content) {
  if (content.type === 'image_file') {
    const fileContent = await openai.files.content(content.image_file.file_id);
  }
}

File Search (RAG)

Semantic search with vector stores. 10,000 files max (v2, was 20 in v1). Pricing: $0.10/GB/day (1GB free).

// Create vector store
const vs = await openai.beta.vectorStores.create({ name: "Docs" });
await openai.beta.vectorStores.files.create(vs.id, { file_id: "file_123" });

// Wait for indexing
let store = await openai.beta.vectorStores.retrieve(vs.id);
while (store.status === 'in_progress') {
  await new Promise(r => setTimeout(r, 2000));
  store = await openai.beta.vectorStores.retrieve(vs.id);
}

// Use in assistant
tool_resources: { file_search: { vector_store_ids: [vs.id] } }

⚠️ Wait for status: 'completed' before using

Function Calling

Submit tool outputs when run.status === 'requires_action':

if (run.status === 'requires_action') {
  const toolCalls = run.required_action.submit_tool_outputs.tool_calls;
  const outputs = toolCalls.map(tc => ({
    tool_call_id: tc.id,
    output: JSON.stringify(yourFunction(JSON.parse(tc.function.arguments))),
  }));

  run = await openai.beta.threads.runs.submitToolOutputs(thread.id, run.id, {
    tool_outputs: outputs,
  });
}

File Formats

Code Interpreter: .c, .cpp, .csv, .docx, .html, .java, .json, .md, .pdf, .php, .pptx, .py, .rb, .tex, .txt, .css, .jpeg, .jpg, .js, .gif, .png, .tar, .ts, .xlsx, .xml, .zip (512MB max)

File Search: .c, .cpp, .docx, .html, .java, .json, .md, .pdf, .php, .pptx, .py, .rb, .tex, .txt, .css, .js, .ts, .go (512MB max)

---

Known Issues

1. Thread Already Has Active Run

Error: 400 Can't add messages to thread_xxx while a run run_xxx is active.

Fix: Cancel active run first: await openai.beta.threads.runs.cancel(threadId, runId)

2. Run Polling Timeout / Incomplete Status

Error: OpenAIError: Final run has not been received

Why It Happens: Long-running tasks may exceed polling windows or finish with incomplete status Prevention: Handle incomplete runs gracefully

try {
  const stream = await openai.beta.threads.runs.stream(thread.id, { assistant_id });
  for await (const event of stream) {
    if (event.event === 'thread.message.delta') {
      process.stdout.write(event.data.delta.content?.[0]?.text?.value || '');
    }
  }
} catch (error) {
  if (error.message?.includes('Final run has not been received')) {
    // Run ended with 'incomplete' status - thread can continue
    const run = await openai.beta.threads.runs.retrieve(thread.id, runId);
    if (run.status === 'incomplete') {
      // Handle: prompt user to continue, reduce max_completion_tokens, etc.
    }
  }
}

Source: GitHub Issues #945, #1306, #1439

3. Vector Store Not Ready Using vector store before indexing completes. Fix: Poll vectorStores.retrieve() until status === 'completed' (see File Search section)

4. File Upload Format Issues Unsupported file formats cause silent failures. Fix: Validate file extensions before upload (see File Formats section)

5. Vector Store Upload Documentation Incorrect

Error: No 'files' provided to process

Why It Happens: Official documentation shows incorrect usage of uploadAndPoll Prevention: Wrap file streams in { files: [...] } object

// ✅ Correct
await openai.beta.vectorStores.fileBatches.uploadAndPoll(vectorStoreId, {
  files: fileStreams
});

// ❌ Wrong (shown in official docs)
await openai.beta.vectorStores.fileBatches.uploadAndPoll(vectorStoreId, fileStreams);

Source: GitHub Issue #1337

6. Reasoning Models Reject Temperature Parameter

Error: Unsupported parameter: 'temperature' is not supported with this model

Why It Happens: When updating assistant to o3-mini/o1-preview/o1-mini, old temperature settings persist Prevention: Explicitly set temperature to null

await openai.beta.assistants.update(assistantId, {
  model: 'o3-mini',
  reasoning_effort: 'medium',
  temperature: null,  // ✅ Must explicitly clear
  top_p: null
});

Source: GitHub Issue #1318

7. uploadAndPoll Returns Vector Store ID Instead of Batch ID

Error: Invalid 'batch_id': 'vs_...'. Expected an ID that begins with 'vsfb_'.

Why It Happens: uploadAndPoll returns vector store object instead of batch object Prevention: Use alternative methods to get batch ID

// Option 1: Use createAndPoll after separate upload
const batch = await openai.vectorStores.fileBatches.createAndPoll(
  vectorStoreId,
  { file_ids: uploadedFileIds }
);

// Option 2: List batches to find correct ID
const batches = await openai.vectorStores.fileBatches.list(vectorStoreId);
const batchId = batches.data[0].id; // starts with 'vsfb_'

Source: GitHub Issue #1700

8. Vector Store File Delete Affects All Stores Warning: Deleting a file from one vector store removes it from ALL vector stores

// ❌ This deletes file from VS_A, VS_B, AND VS_C
await openai.vectorStores.files.delete('VS_A', 'file-xxx');

Why It Happens: SDK or API bug - delete operation has global effect Prevention: Avoid sharing files across multiple vector stores if selective deletion is needed Source: GitHub Issue #1710

9. Memory Leak in Large File Uploads (Community-sourced) Source: GitHub Issue #1052 | Status: OPEN Impact: ~44MB leaked per 22MB file upload in long-running servers Why It Happens: When uploading large files from streams (S3, etc.) using vectorStores.fileBatches.uploadAndPoll, memory may not be released after upload completes Verified: Maintainer acknowledged, reduced in v4.58.1 but not eliminated Workaround: Monitor memory usage in long-lived servers; restart periodically or use separate worker processes

10. Thread Already Has Active Run - Race Condition (Community-sourced) Enhancement to Issue #1: When canceling an active run, race conditions may occur if the run completes before cancellation

async function createRunSafely(threadId: string, assistantId: string) {
  // Check for active runs first
  const runs = await openai.beta.threads.runs.list(threadId, { limit: 1 });
  const activeRun = runs.data.find(r =>
    ['queued', 'in_progress', 'requires_action'].includes(r.status)
  );

  if (activeRun) {
    try {
      await openai.beta.threads.runs.cancel(threadId, activeRun.id);

      // Wait for cancellation to complete
      let run = await openai.beta.threads.runs.retrieve(threadId, activeRun.id);
      while (run.status === 'cancelling') {
        await new Promise(r => setTimeout(r, 500));
        run = await openai.beta.threads.runs.retrieve(threadId, activeRun.id);
      }
    } catch (error) {
      // Ignore "already completed" errors - run finished naturally
      if (!error.message?.includes('completed')) throw error;
    }
  }

  return openai.beta.threads.runs.create(threadId, { assistant_id: assistantId });
}

Source: OpenAI Community Forum

See references/top-errors.md for complete catalog.

Relationship to Other Skills

openai-api (Chat Completions): Stateless, manual history, direct responses. Use for simple generation.

openai-responses (Responses API): ✅ Recommended for new projects. Better reasoning, modern MCP integration, active development.

openai-assistants: ⚠️ Deprecated H1 2026. Use for legacy apps only. Migration: references/migration-to-responses.md

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v1 to v2 Migration

v1 deprecated: Dec 18, 2024

Key Changes: retrieval → file_search, vector stores (10k files vs 20), 256k instructions (vs 32k), message-level file attachments

See references/migration-from-v1.md

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Templates: templates/basic-assistant.ts, code-interpreter-assistant.ts, file-search-assistant.ts, function-calling-assistant.ts, streaming-assistant.ts

References: references/top-errors.md, thread-lifecycle.md, vector-stores.md, migration-to-responses.md, migration-from-v1.md

Related Skills: openai-responses (recommended), openai-api

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Last Updated: 2026-01-21 Package: openai@6.16.0 Status: Production Ready (⚠️ Deprecated - Sunset August 26, 2026) Changes: Added 6 new known issues (vector store upload bugs, o3-mini temperature, memory leak), enhanced streaming error handling