/image-generation

name: image-generation
description: Generate images from text prompts (and optionally edit/remix input images). Use when the user asks to create, generate, draw, render, or edit an image, illustration, logo, icon, diagram, slide, photo, animated GIF, or SVG.

Image Generation

Generate images via Letta's hosted endpoint `POST /v1/images/generations`. The API usually returns base64 image bytes, but some providers return signed image URLs; save either form to a local image file before replying.

Example

Generate the image, save it locally, then show it inline:

base_url="${LETTA_BASE_URL%/}"

curl -sS -X POST "$base_url/v1/images/generations" \
  -H "Authorization: Bearer $LETTA_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"provider":"gemini","prompt":"a friendly robot mascot waving, flat vector logo, mint green background","n":1}' \
  > image-response.json

python3 - <<'PY'
import base64, json, urllib.request

with open("image-response.json") as f:
    response = json.load(f)

image = response["images"][0]
if image.get("b64_json"):
    data = base64.b64decode(image["b64_json"])
else:
    data = urllib.request.urlopen(image["url"]).read()

with open("robot-mascot.png", "wb") as f:
    f.write(data)

print("saved robot-mascot.png")
PY

In Bash tools launched by Letta Code, use the runtime-provided `LETTA_BASE_URL` and `LETTA_API_KEY` together for Letta API calls. Build URLs relative to `${LETTA_BASE_URL%/}` and send `Authorization: Bearer $LETTA_API_KEY`. Do not hardcode `https://api.letta.com`: Desktop and remote runtimes may provide a proxy base URL, and the credential may only be valid through that URL. If either variable is missing, the user needs to authenticate with Letta Cloud (or provide a Letta API key); do **not** ask for an OpenAI/Gemini provider key. This endpoint also does not use `/connect` BYOK providers — the only `provider` values supported here are `flux`, `gemini`, and `openai`.

Then **show the image to the user** by embedding the saved file in your reply:

Here's the mascot:

![a friendly robot mascot waving, flat vector logo](./robot-mascot.png)

The Letta Code UI renders local file paths in markdown image tags, so the image appears inline. **Always display generated images this way** — don't just report the path, and never paste the raw base64 / a `data:` URI. The markdown path must match where you saved the file. For `n > 1`, save each image to its own file and embed each on its own line. Keep credit amounts and billing metadata out of user-facing replies and captions unless the user asks about cost. When asked, read `billing.credits_charged` from the saved response.

Request body

| Field | Type | Notes | |-------|------|-------| | `provider` | `"flux"` \| `"gemini"` \| `"openai"` | Required. | | `prompt` | string | Required, 1–32000 chars. | | `model` | string | Optional; defaults per provider (below). | | `n` | int 1–4 | Optional, default 1. Request variations in one call. | | `size` | string | Optional, e.g. `"1024x1024"` (OpenAI). | | `quality` | `low`\|`medium`\|`high`\|`xhigh`\|`max`\|`auto` | Optional (OpenAI; higher = more credits; `xhigh`/`max` need GPT Image 2.6). | | `background` | `auto`\|`opaque`\|`transparent` | Optional (OpenAI). Transparent works with png, webp and svg. | | `complexity` | `low`\|`medium`\|`high` | Optional (OpenAI GPT Image 2.6). How much the model plans before rendering; defaults to `high`. | | `output_format` | `png`\|`jpeg`\|`webp`\|`gif`\|`svg` | Optional (OpenAI). `gif` and `svg` need GPT Image 2.6; see below. | | `frame_count` / `frame_duration_ms` | int 2–16 / int 20–2000 | Optional, `gif` only. Defaults 9 frames, 200 ms. | | `svg` | `{ "model"?, "reasoning"?: { "effort" } }` | Optional, `svg` only. Model that writes the SVG: `gpt-6.1-terra` (default), `gpt-6.1-sol`, `gpt-6-luna` or `gpt-6-astra`. | | `input_images` | string[] (max 14) | Optional. Base64 **data URLs** for edit/remix. | | `markup_image` | string | Optional (OpenAI edits). Base64 data URL of a transparent annotation layer marking where to change the first input image. | | `seed` | int | Optional. |

| Provider | Default model | Use for | |----------|---------------|---------| | `flux` | `flux-2-pro` | Default for normal text-to-image. High-quality general image generation; commonly returns signed URLs. | | `gemini` | `gemini-3-pro-image` | Strong prompt adherence, image editing/remix. | | `openai` | `gpt-image-2.6-flare` | Photoreal output, explicit `size`/`quality`, animated GIFs, SVG vectors, markup-guided edits. Use `gpt-image-2.6-sunburst` for detailed work and consistency across edits. |

Default to `flux` for normal text-to-image requests. Use `gemini` when the user provides input images or wants image editing/remix. Use `openai` when the user wants photoreal output, a specific size/quality, an animated GIF, an SVG, or an edit guided by a marked-up region.

Response

{
  "provider": "gemini",
  "model": "gemini-3-pro-image",
  "images": [{ "b64_json": "<base64>", "mime_type": "image/png" }],
  "billing": { "credits_charged": 12, "...": "..." }
}

Each `images[]` entry has either `b64_json` or `url`, plus `mime_type`. Gemini always returns `b64_json`. Flux commonly returns a signed `url`; download it to your local image file immediately because signed URLs expire. If OpenAI returns a `url`, download that URL instead of base64-decoding.

Editing / remixing images

Pass source images in `input_images` as base64 **data URLs** (`data:<mime>;base64,<data>`) and describe the edit in `prompt`. Gemini handles multi-image edits well. To build a data URL from a local file:

DATA_URL="data:image/png;base64,$(base64 < input.png | tr -d '\n')"

Prompting (applies to every provider)

Write the prompt like a brief for the image you need, then inspect the result and refine one thing at a time.

1. **Define the result.** Name the subject and the intended use (product photo, ad, dia