gpt-5.6-terra

Quick example

curl https://api.reapi.ai/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.6-terra",
    "messages": [
      { "role": "user", "content": "Implement the change in the linked issue, with tests." }
    ],
    "reasoning_effort": "medium",
    "max_completion_tokens": 8192,
    "stream": true
  }'

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api.reapi.ai/v1",
)

stream = client.chat.completions.create(
    model="gpt-5.6-terra",
    messages=[{"role": "user", "content": "Implement the change in the linked issue, with tests."}],
    reasoning_effort="medium",
    max_completion_tokens=8192,
    stream=True,
)
for chunk in stream:
    delta = chunk.choices[0].delta.content
    if delta:
        print(delta, end="")

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: "YOUR_API_KEY",
  baseURL: "https://api.reapi.ai/v1",
});

const stream = await client.chat.completions.create({
  model: "gpt-5.6-terra",
  messages: [{ role: "user", content: "Implement the change in the linked issue, with tests." }],
  reasoning_effort: "medium",
  max_completion_tokens: 8192,
  stream: true,
});

for await (const chunk of stream) {
  process.stdout.write(chunk.choices[0]?.delta?.content ?? "");
}

package main

import (
    "bytes"
    "encoding/json"
    "fmt"
    "io"
    "net/http"
)

func main() {
    body, _ := json.Marshal(map[string]any{
        "model": "gpt-5.6-terra",
        "messages": []map[string]string{
            {"role": "user", "content": "Implement the change in the linked issue, with tests."},
        },
        "reasoning_effort":       "medium",
        "max_completion_tokens":  8192,
    })
    req, _ := http.NewRequest("POST",
        "https://api.reapi.ai/v1/chat/completions", bytes.NewReader(body))
    req.Header.Set("Authorization", "Bearer YOUR_API_KEY")
    req.Header.Set("Content-Type", "application/json")

    resp, _ := http.DefaultClient.Do(req)
    defer resp.Body.Close()
    out, _ := io.ReadAll(resp.Body)
    fmt.Println(string(out))
}

Authentication

Chat models are served from the api.reapi.ai gateway, which has its own console and its own key. Create the key there, then send it as a bearer token:

Authorization: Bearer YOUR_API_KEY

Endpoint

POST /v1/chat/completions

Base URL https://api.reapi.ai. The wire format is OpenAI-compatible, so the same SDKs work once you swap the base URL, the key and the model string.

Request body

model — string, required

Must be gpt-5.6-terra exactly. There is no alias for this tier — the bare gpt-5.6 id routes to the frontier model instead.

messages — array, required

Conversation history, each entry an object with role and content. Roles are system, user, assistant and tool. Text and image parts are supported — see Image input.

max_completion_tokens — integer

Upper bound on generated tokens for this response, reasoning tokens included. The documented maximum output is 128,000 tokens.

reasoning_effort — string, default "medium"

How much the model thinks before answering. See Reasoning effort.

stream — boolean, default false

When true, tokens arrive as server-sent events terminated by data: [DONE]. At the default effort the model thinks before it answers, so streaming is what keeps an interactive surface from looking stalled.

tools / tool_choice — optional

Function definitions and the selection strategy. Functions, web search, file search and computer use are all available on this family, and this generation adds programmatic tool calling.

response_format — object, optional

Constrains the answer's shape, including a JSON schema for machine-consumed output.

group — string, default "default"

Token group on the gateway. Leave it at default unless your account has been given another group to route through.

Reasoning effort

Six rungs, and unlike some families these do not collapse into one another — each is a distinct behaviour. The default is medium: OpenAI's docs state that "if you omit reasoning.effort, GPT-5.6 defaults to medium in both modes."

There is no minimal on this family.

This tier is where the default is genuinely the right starting point. Sweep low for speed on planning-shaped work and high when a route needs complex debugging; if your evals keep choosing xhigh or max, that route belongs on the frontier tier instead.

Image input

This generation accepts images at their original dimensions, with original or auto image detail — no resizing step required before a screenshot or scan goes in. Output is text only.

Pricing dimensions

Billing is per token, in USD, against your api.reapi.ai balance, with separate input and output rates. Three things to keep in mind:

• Reasoning tokens bill as output. The default effort is medium, so a request that omits the field is paying for a reasoning pass.
• Effort is the first lever, and on this family every rung is real — a middle setting buys a middle cost.
• The tier is the second lever. All three GPT-5.6 tiers share this context window, this output ceiling, this effort ladder and this endpoint, so moving between them changes reasoning depth and price, not capability surface.

Both token rates sit 20% below OpenAI's published per-token rate, on input and output alike. Current numbers are on the model page and api.reapi.ai/pricing — those tables are the canonical source, not this page.

Response shape

Non-streaming (stream: false)

{
  "id": "chatcmpl-...",
  "object": "chat.completion",
  "created": 1785000000,
  "model": "gpt-5.6-terra",
  "choices": [
    {
      "index": 0,
      "message": { "role": "assistant", "content": "..." },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 1204,
    "completion_tokens": 860,
    "total_tokens": 2064
  }
}

usage.completion_tokens includes reasoning tokens, so it is the number to reconcile a bill against. On OpenAI's own Responses API the split is reported under output_tokens_details.reasoning_tokens.

Streaming (stream: true)

Server-sent events, each data: line carrying a chat.completion.chunk with the incremental text in choices[0].delta.content, terminated by data: [DONE].

Errors

Failures use the gateway's standard envelope. See the errors catalog for the full code list. Common cases:

Tips

• Leave the default alone first. medium is what OpenAI calls the well-balanced point, and this tier is priced for it.
• Then sweep in both directions on a real route — low for speed, high for hard debugging — and keep whichever your evals prefer.
• Escalate on evidence, not instinct. A route that always wants xhigh or max is telling you it belongs one tier up.
• Use a JSON schema for agent steps whose output another step consumes.
• Budget for the reasoning pass in max_completion_tokens, not just the answer.
• The window is the frontier tier's. Choosing this tier does not shrink what the model can see.

Related

• GPT-5.6 Terra model page — current rates
• GPT-5.6 Sol — the frontier tier above it
• GPT-5.6 Luna — the volume tier below it
• Errors catalog
• Authentication
• Quickstart