6.3
- Startup time reduction
- Tightening and cleanup of numeric types
- Sealing contracts for row polymorphic types
- `define-new-subtype`
- More robust compound pair operations optimizations
- Redesign of top-level support, using trampolining macros
- Static contract caching more conservative, causes contract generation slowdowns
- Experimental unit support
- `typed/racket/unsafe`, with `unsafe-require/typed` and `unsafe-provide`
6.2
- Use submodules to avoid allocating contract wrappers when not needed.
- Class types and contract generation are significantly improved, but still experimental.
- Many types for GUI classes added.
- Tests on let-bound variables now refine the type of what was bound to them.
- DrRacket tooltips for types and type errors.
- Support for prefab structs.
- Types for a variety of libraries, including `rackunit` and `json`.
6.1.1
- Exception handling is now sound. Broke existing programs (e.g. marketplace).
- More types for GUI and framework.
- Support for casts and predicates in typed regions.
6.1
- Inference speedups.
- Support for contracted functions in the base environment.
- Better keyword support.
6.0.1
- Types for classes (including row types, sealing contracts, etc).
  Still experimental.  
- Contracts are now optimized; in particular, redundant contracts are omitted
- Filters work with conditions that raise errors, as in the pattern
  (begin (unless (number? x) (error 'fail))
         (add1 x))
- Types are now pretty-printed
- Add prefix-style function types and `->*` function type constructor
- Support syntactic forms without : (such as let, lambda, for, etc)
- Type aliases support arbitrary mutual recursion
- Inform check-syntax about expansion results
- Add `typed/untyped-utils` library
- Add `typed/syntax/stx`, `typed/pict`, 
- Significant test suite improvments
- Improved support for `Struct-Type` values
- Support keyword function definitions without annotation.
- Handle forward references in un-annotated definitions
- Improve type inference for `letrec`-bound variables
6.0
- Support for `define-type', `struct:', `make-predicate', etc. at the REPL
- Performance work: optimized subtyping
- Make `struct:' have the correct bindings in struct info
- Use pairs for objects on arrow types
- Split off `recover-source-syntax' into a separate package and generalized it
- Lots of doc improvements
- Lots of error message improvements
- Split into multiple packages
5.3.4
- Moved Optimization Coach to the package system
- Multiple fixes to polydots
5.3.3
  No changes
5.3.2
- Added types for control operators
- Added `typed/untyped-utils`
5.3.1
- Revised handling of `Any` exported to untyped code
- Added `cast`
- Correctly compute variance of polymorphic type application
5.3
- Keyword and optional arguments
- Faster startup
- Random testing of the numeric tower
5.2.1
- Inference of functions with keyword arguments
- `typecheck-fail' for explicit creation of type errors
- Extensive documentation of typed numeric tower
5.2
- Performance work: delayed environment evaluation
- Support `racket'-style optional arguments
- Changes to support new-style keyword argument expansion
