Impossibl

Access 76 Impossibl models through Mastra's model router. Authentication is handled automatically using the IMPOSSIBL_API_KEY environment variable.

Learn more in the Impossibl documentation.

.env

IMPOSSIBL_API_KEY=your-api-key

src/mastra/agents/my-agent.ts

import { Agent } from "@mastra/core/agent";

const agent = new Agent({
  id: "my-agent",
  name: "My Agent",
  instructions: "You are a helpful assistant",
  model: "impossibl/anthropic/claude-fable-5"
});

// Generate a response
const response = await agent.generate("Hello!");

// Stream a response
const stream = await agent.stream("Tell me a story");
for await (const chunk of stream) {
  console.log(chunk);
}

note

Mastra uses the OpenAI-compatible /chat/completions endpoint. Some provider-specific features may not be available. Check the Impossibl documentation for details.

Models

76 available models

Model	Context	Tools	Reasoning	Image	Audio	Video	Input $/1M	Output $/1M
impossibl/anthropic/claude-fable-5	1.0M						$10	$50
impossibl/anthropic/claude-haiku-4-5	200K						$1	$5
impossibl/anthropic/claude-opus-4-5	200K						$5	$25
impossibl/anthropic/claude-opus-4-6	1.0M						$5	$25
impossibl/anthropic/claude-opus-4-7	1.0M						$5	$25
impossibl/anthropic/claude-opus-4-8	1.0M						$5	$25
impossibl/anthropic/claude-sonnet-4-5	200K						$3	$15
impossibl/anthropic/claude-sonnet-4-6	1.0M						$3	$15
impossibl/anthropic/claude-sonnet-5	1.0M						$2	$10
impossibl/cerebras/gpt-oss-120b	131K						$0.35	$0.75
impossibl/deepseek/deepseek-v4-flash	1.0M						$0.19	$0.51
impossibl/deepseek/deepseek-v4-pro	1.0M						$2	$3
impossibl/fireworks/glm-5.2	1.0M						$1	$4
impossibl/fireworks/gpt-oss-120b	131K						$0.15	$0.60
impossibl/fireworks/gpt-oss-20b	131K						$0.07	$0.30
impossibl/google/gemini-2.5-flash	1.0M						$0.30	$3
impossibl/google/gemini-2.5-flash-lite	1.0M						$0.10	$0.40
impossibl/google/gemini-2.5-pro	1.0M						$1	$10
impossibl/google/gemini-3.1-flash-lite	1.0M						$0.25	$2
impossibl/google/gemini-3.1-pro-preview	1.0M						$2	$12
impossibl/google/gemini-3.5-flash	1.0M						$2	$9
impossibl/google/gemini-3.5-flash-lite	1.0M						$0.30	$3
impossibl/google/gemini-3.6-flash	1.0M						$2	$8
impossibl/groq/gpt-oss-120b	131K						$0.15	$0.60
impossibl/groq/gpt-oss-20b	131K						$0.07	$0.30
impossibl/moonshotai/kimi-k3	1.0M						$3	$15
impossibl/openai/gpt-3.5-turbo	16K						$0.50	$2
impossibl/openai/gpt-4-turbo	128K						$10	$30
impossibl/openai/gpt-4.1	1.0M						$2	$8
impossibl/openai/gpt-4.1-mini	1.0M						$0.40	$2
impossibl/openai/gpt-4.1-nano	1.0M						$0.10	$0.40
impossibl/openai/gpt-4o	128K						$3	$10
impossibl/openai/gpt-4o-mini	128K						$0.15	$0.60
impossibl/openai/gpt-5	400K						$1	$10
impossibl/openai/gpt-5-codex	400K						$1	$10
impossibl/openai/gpt-5-mini	400K						$0.25	$2
impossibl/openai/gpt-5-nano	400K						$0.05	$0.40
impossibl/openai/gpt-5-pro	400K						$15	$120
impossibl/openai/gpt-5.1	400K						$1	$10
impossibl/openai/gpt-5.1-codex	400K						$1	$10
impossibl/openai/gpt-5.1-codex-mini	400K						$0.25	$2
impossibl/openai/gpt-5.2	400K						$2	$14
impossibl/openai/gpt-5.2-codex	400K						$2	$14
impossibl/openai/gpt-5.3-codex	400K						$2	$14
impossibl/openai/gpt-5.4	1.1M						$3	$15
impossibl/openai/gpt-5.4-mini	400K						$0.75	$5
impossibl/openai/gpt-5.4-nano	400K						$0.20	$1
impossibl/openai/gpt-5.4-pro	1.1M						$30	$180
impossibl/openai/gpt-5.5	1.1M						$5	$30
impossibl/openai/gpt-5.5-pro	1.1M						$30	$180
impossibl/openai/gpt-5.6-luna	1.1M						$0.20	$1
impossibl/openai/gpt-5.6-sol	1.1M						$5	$30
impossibl/openai/gpt-5.6-terra	1.1M						$2	$12
impossibl/openai/o1	200K						$15	$60
impossibl/openai/o3	200K						$2	$8
impossibl/openai/o3-mini	200K						$1	$4
impossibl/openai/o4-mini	200K						$1	$4
impossibl/qwen/qwen3.6-flash	1.0M						$0.25	$2
impossibl/qwen/qwen3.7-max	1.0M						$3	$8
impossibl/qwen/qwen3.7-plus	1.0M						$0.40	$2
impossibl/qwen/qwen3.8-max-preview	1.0M						$3	$8
impossibl/thinkingmachines/inkling	66K						$2	$5
impossibl/xai/grok-4.20-0309-non-reasoning	1.0M						$1	$3
impossibl/xai/grok-4.20-0309-reasoning	1.0M						$1	$3
impossibl/xai/grok-4.3	1.0M						$1	$3
impossibl/xai/grok-4.5	500K						$2	$6
impossibl/xai/grok-build-0.1	256K						$1	$2
impossibl/xiaomi/mimo-v2.5	1.0M						$0.14	$0.28
impossibl/zai/glm-4.5	131K						$0.60	$2
impossibl/zai/glm-4.5-air	131K						$0.20	$1
impossibl/zai/glm-4.6	205K						$0.60	$2
impossibl/zai/glm-4.7	205K						$0.60	$2
impossibl/zai/glm-5	205K						$1	$3
impossibl/zai/glm-5-turbo	200K						$1	$4
impossibl/zai/glm-5.1	200K						$1	$4
impossibl/zai/glm-5.2	1.0M						$1	$4

Model availability, capabilities, context windows, and pricing are sourced from models.dev and may change.

Advanced configuration

Custom headers

src/mastra/agents/my-agent.ts

const agent = new Agent({
  id: "custom-agent",
  name: "custom-agent",
  model: {
    url: "https://api.impossibl.com/v1",
    id: "impossibl/anthropic/claude-fable-5",
    apiKey: process.env.IMPOSSIBL_API_KEY,
    headers: {
      "X-Custom-Header": "value"
    }
  }
});

Dynamic model selection

src/mastra/agents/my-agent.ts

const agent = new Agent({
  id: "dynamic-agent",
  name: "Dynamic Agent",
  model: ({ requestContext }) => {
    const useAdvanced = requestContext.task === "complex";
    return useAdvanced
      ? "impossibl/zai/glm-5.2"
      : "impossibl/anthropic/claude-fable-5";
  }
});