Currently there is no guarantee of this.
Possibilities:
All the same: The lexical syntax for numbers accepted by string->number and read, as well as the corresponding syntax of literal numbers in programs, must be the same.
All the same at run time: The lexical syntax for numbers accepted by string->number and read must be the same, but the relationship with the the corresponding syntax of literal numbers in programs is unspecified.
All potentially different: The relationships between lexical syntax for numbers accepted by string->number and read, as well as the corresponding syntax of literal numbers in programs, is unspecified.
The WG voted to adopt this proposal.
That is, we adopted the proposal that all three support the same syntax.
More from Vincent:
The syntactic issues relate to such things as whether S, F, D, and L are valid ("the implementation may accept...", p. 32). Pragmatic issues include whether integer or other literals might overflow (on a bignum-less implementation), whether or not the implementation applies the same restrictions, described at the bottom of p. 37) to string->number, read, and literals in source programs; the default precision if the E exponent marker is used; and numerical roundoff on input conversion (whether, e.g., (= (string->number? 0.1) 0.1) is defined to be true).
Vincent formerly supported the All the same choice, but now supports All the same at run time.