SAPI SAPI comes in mulitple varieties:
SAPI 5.1
Getting SAPI 5.1: Overview
The following are notes TOOGAM had made:
  • Users of Microsoft Windows XP need to do nothing. It is installed w/ WinXP.
  • Office XP has the SAPI 5.1 files built in.
  • Users of Microsoft Windows 98, NT4, 2K, and Me can download it if they don't already have it installed. Further details for this are below.
  • As far as I know, SAPI 5+ doesn't exist for any other Operating Systems, including Windows 95 (although there is a SAPI 4 did exist for Windows 95).
Requirements: Archived version of old SAPI page mentioned requirements of
  • Windows NT 4.0 Workstation or Server, Service Pack 6a, English, Japanese, or Simplified Chinese versions. Also IE 5.5 is needed for NT 4.0.
  • Windows 98 with MS IE 5.0 or later.
  • "Windows 95 or earlier is not supported."
Other requiremnts were also listed on the page for developers. "In general, any 32-bit C compiler will work for writing SAPI applications." SAPI automated can be used with languges and compilers that support OLE automation, with Visual Basic 6.0 given as a minimum version of that environment. VB 6.0, VC++ 6.0 SP3+ are needed for some examples, and MS VS .NET needed for C# examples.
Redistribution:

Archive.Org's June 23, 2006 version of "Microsoft Speech - Redistributable Files".

Q320207: How to redistribute SAPI 5.1 core components refers to a page that is down, but still visible: July 4, 2007 archived version of SAPI download page. By October 5, 2007, the page was removed from Microsoft's site. The "Redist.: All" link pointed to here.

Main Files
Files of use to end user
Voices
I believe these voice packages also some with basic SAPI software that enables them to be used.
msttss22L (the letters of which probably refer to Microsoft Text To Speech: Sam Language)
A third party site says: "msttss22L.exe is the Microsoft Speech Redistributable installer." ShadiSoft Multiple Voice Support identifies this as the Microsoft Sam voice (and also has Mary, and Mike, all as separate downloads). (Mike is msttsm22l.exe and mary is msttsf22l.exe. The f in the filename of Mary's voice likely refers to her voice being named the "female" voice.)
Redistributable: Mike and Mary file
Other voices
I read other voices came with Office XP (by L&H, not MS?)
Documentation (sapi.chm from SAPI 5.1)
Other client software
Developer Software
Speech SDK 5.1 file
Speech SDK 5.1 Language Pack file
"Speech 5.1 SDK Redistributables: All file"
Speech Utilities for Microsoft Speech Technologies
A "Download details" page (Seperate downloads, requires "Windows Server 2003; Windows XP"
SAPI 4.0a
SAPI 4.0a (spchapi.EXE) (local, lowercased)
SAPI 5.3
anna mp3
SALT