StackPrism

Web frameworks

FastAPI vs Flask

Both are open source: FastAPI under MIT, Flask under BSD-3-Clause. OSV.dev lists 1 advisory from the last 12 months for Flask and none for FastAPI.

Last checked against PyPI, deps.dev, OSV.dev and CISA KEV.

Check my repoDesign a stack with either

Side by side

Every value links to its source. Where a row doesn’t apply to one of them, the cell says why.

Support and releases
FastAPIFlask
Latest release

0.143.3

Released Oct 16, 2026

PyPI

3.1.3

Released Feb 19, 2026

PyPI

Releases in the last 12 months

93 releases

fastapi on PyPI

PyPI

1 release

flask on PyPI

PyPI

Security
FastAPIFlask
Advisories published in the last 12 months

None

For fastapi

OSV.dev

1, worst rated low

For flask

OSV.dev

OpenSSF Scorecard

No Scorecard published

7.1 / 10

pallets/flask, Aug 24, 2026

Scorecard

Licence and hosting
FastAPIFlask
Licence

MIT

Open source (permissive)

deps.dev

BSD-3-Clause

Open source (permissive)

deps.dev

How you run it

Your own Python app server (ASGI)

Your own Python app server (WSGI)

Adoption
FastAPIFlask
GitHub stars

103K

fastapi/fastapi

GitHub

75K

pallets/flask

GitHub

  • Advisory counts cover every version, old ones included, and a heavily used, well-audited project often has more. Check the versions you run with the dependency check.

Which fits your constraints

Read across for what matters to you. Each answer comes from the data above or the project’s licence and hosting options.

How FastAPI and Flask fit common constraints
FastAPIFlask
An open-source licence

Yes: MIT

Yes: BSD-3-Clause

What each is good at

FastAPI

Modern Python framework for building APIs with type hints

Strengths

  • Extremely fast performance (on par with Node/Go)
  • Automatic API documentation (OpenAPI/Swagger)
  • Type hints for validation and IDE support
  • Async/await support out of the box
  • Easy to learn and use

Trade-offs

  • Younger ecosystem than Django/Flask
  • Less built-in features than Django
  • Fewer third-party integrations

Common uses

  • REST APIs
  • Microservices
  • Machine learning APIs
  • High-performance backends

Flask

Lightweight Python micro framework: routing and templates, the rest via extensions

Strengths

  • Small core that is quick to learn
  • Pick your own ORM, auth and validation libraries
  • Large extension ecosystem (Flask-SQLAlchemy, Flask-Login)
  • Mature and stable (first released in 2010)

Trade-offs

  • No built-in ORM, admin or authentication
  • WSGI-based: async views are supported, but each request still holds a worker
  • No built-in request validation
  • Larger apps need their own structure conventions

Common uses

  • Small web apps
  • REST APIs
  • Prototypes
  • Internal tools

From StackPrism’s curated notes. Pricing isn’t covered here: it changes often, so check each vendor’s pricing page.

When teams weigh these two

Both are small Python frameworks often used for APIs. FastAPI is built on ASGI, with async support, request validation from type hints and automatic OpenAPI docs; Flask is a WSGI micro framework with a large extension ecosystem and a longer history.

How this comparison works

Release lines and end-of-life dates come from endoflife.date, release counts from deps.dev’s publish dates, and advisories from OSV.dev, counted once per flaw even when it’s listed under several ids, and checked against CISA’s list of vulnerabilities known to be exploited. Status and incident history come from each vendor’s public status feed; licences from each project’s licence file or the vendor’s licensing page, linked in the table.

The data refreshes every few hours and the time it was checked is shown above. There’s no pricing and no overall winner: which one fits depends on your constraints. To see how the versions you actually run hold up, check your repo.

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