I saw people discussing his changes over time on FB:
" Here exist assorted Jews in the absolutely unassimilated state, with their ancestral beards, skull-caps, and general costumes—which make them very pictureseque, and not nearly so offensive as the strident, pushing Jews who affect clean shaves and American dress. In this particular section, where Hebrew books are vended from pushcarts, and patriarchal rabbis totter in high hats and frock coats, there are far less offensive faces than in the general subways of the town—probably because most of the pushing commercial Jews are from another colony where the blood is less pure. It is now definitely known that many allegedly Semitic types of today are not in reality Semitic or even white at all, but derived from Asiatic Tatar-Mongoloids who were Judaised by missionaries before their entrance into Central Europe from the Thibetan plateaux in the 8th or 9th century A.D. Of these are the queer-eyed, yellow-red, thick-lipped flat-nosed types seen in Providence’s North End and in many parts of New York. These Rivington-Streeters are altogether different, and when they depart from the Semitic type, the variation is toward the Aryan rather than toward the Asiatic."
H. P. Lovecraft to Lillian Clark, 29 Sep 1924 (Letters from New York 74)
But during his marriage:
" But on the other hand, the Jewish radius contains many elements biologically equal—& perhaps superior to anything we can boast. Spinoza—Einstein—Disraeli—Mendelssohn—Maimonides, & so on. Now any biologist knows that innate racial identity plays a damn small part in the moulding of cultural details. The culture a man has is now what is blood has determined, but what the massed impressions & traditions he has received have given him. Jewish culture is not a product of blood, but of historic accident. So is ours. Bring a Jew up in Aryan culture, & he will in the main be a real Aryan unless Jewish ancestral influences get at him…& a good or bad Aryan according to his intrinsic biological status. Conversely, any of us could be a Jew if brought up among Jews & severed wholly from our own inheritance. It is, therefore, not at all important to maintain rigid barriers against every trace of Jewish blood when our real & legitimate object is merely to exclude Jewish cultural influences (which are hostile & unassimilable) from our national life. So long as a man has been brought up in our tradition & no other, & retains no vestiges of alien perspective & thought-habits, it does not make a particle of difference whether or not his ancestry contains a race of blood from any of the other superior races—be it Jewish, Chinese, Polynesian, Japanese, Hindu or American Indian. [The negro & australoid, of course, are another story.] That is, provided his blood-alienage does not involve any marked physiognomical aberrancy of such a sort as to set him apart & drive him back upon his lost alien heritage. It is easy to establish a practical, common-sense classification of persons as to culture-affiliation, even when their blood is not precisely homogenous. Einstein is Jewish—in heritage & loyalties—but what sensible standard would also class as “Jewish” (as outside the Aryan pole) such well-assimilated persons as, for instance, Walter Damrosch, or the publicist Walter Lippmann? These latter two men undeniably think as Aryans—& therefore any sensible committee on classification (to which, under a rational regime of Aryan fascism, all debatable cases would of course be carried) would group them as Aryans. It is amusing to think of the thoroughly Aryan people who would be placed outside as aliens if the strict Nazi test were made worldwide."
H. P. Lovecraft to Alfred Galpin, 25 Jul 1934 (Letters to Alfred Galpin 210-211
Yet after:
" With the high-grade alien races we can adopt a policy of flexible common-sense—discouraging mixture whenever we can, but not clamping down the bars so ruthlessly against every individual of slightly mixed ancestry. As a matter of fact, most of the psychological race-differences which strike us so prominently are cultural rather than biological. If one could take a Japanese infant, alter his features to the Anglo-Saxon type through plastic surgery, & place him with an American family in Boston for rearing—without stemming him that he is not an American—the chances are that in 20 years the result would be a typical American youth with very few instincts to distinguish him from his pure Nordic college-mates. The same is true of other superior alien races including the Jew—although the Nazis persist in acting on a false biological conception. If they were wise in their campaign to get rid of Jewish cultural influences (& a great deal can be said for such a campaign, when the dominance of the Aryan tradition is threatened as in Germany & New York City), they would not emphasize the separatism of the Jew but would strive to make him give up his separate culture & lose himself in the German people. It wouldn't hurt Germany—or alter its essential physical type—to take in all the Jews it now has. (However, that wouldn't work in Poland or New York City, where the Jews are of an inferior strain, & so numerous that they would essentially modify the physical type.)
H. P. Lovecraft to Natalie H. Wooley, 22 Nov 1934, Letters to Robert Bloch and Others 200-201"
I remember reading before that he softened his racist views in general, even regarding African(-American)s and not just Jews. But I couldn't find evidence of this and he did seem to change his mind a lot.
Tagging this whole thread NSFW for old-timey racism.
Okay, so the basics: H. P. Lovecraft was born in 1890, raised in a relatively affluent Yankee household in Providence, Rhode Island, where he had very little contact with anybody that wasn't a white Anglo-Saxon Protestant, and those that were (like the African-American Delilah, who was in the family's employ) were in a servile role. White supremacy and antisemitism was part of the culture he grew up with, and there is evidence of these views from a very tender age. Among Lovecraft's juvenilia written in 1900-1902 is the Poemata Minora in two volumes with illustrations; the illustration for “On the Vanity of Human Ambition” is a Jewish caricature with the inscription: “HIC. HOMO. EST. AVARISSIMVS. ET. TVRPISSIMVS. IUDEVS” (“This man is a greedy and filthy Jew”).
In 1904, Lovecraft's happy home life collapsed. His father had died in an asylum when he was eight, and the family was dependent on his grandfather for financial support; his grandfather's death when Lovecraft was 14 caused the dissolution of the household and the a severe restriction in the circumstances of HPL and his mother. Also, Lovecraft stopped having tutors and attended Hope Street English and Classical High School:
Here I was confronted for the first time with cosmopolitanism. Slater Avenue School is public, but it is rather a neighbourhood affair, with most of its pupils drawn from the old families. But Hope Street is near enough to the "North End" to have considerable Jewish attendance. It was there that I formed my ineradicable aversion to the Semitic race. The Jews were brilliant in their classes—calculatingly & schemingly brilliant—but their ideals were sordid & their manners coarse. I became rather well known as an anti-Semitic before I had been at Hope Street many days. (LRK 74-75)
It says something about the culture of the time that Lovecraft's teachers apparently tolerated this. As it was, HPL's high school attendance was sporadic, due to periods of ill-health and nervous breakdowns or "near-breakdowns"; this prevented him from getting his high school diploma, and ultimately dashed any hopes of attending university.
The next several years Lovecraft was...busied about his own business. He wasn't in school and he wasn't working, the family was living off of the monies left to them from his grandfather's estate. HPL pursued his interested, tried a few courses-by-correspondence, but was fairly reclusive until 1914, when he was recruited for amateur journalism. This brought him into contact with more people again—and inevitably, some of these people were Jewish. He had a particular row with Charles D. Isaacson in 1915, and wrote to his friend Rheinhart Kleiner:
A Jew is capable of infinite nastiness when he seeks revenge, & I believe I shall have ample grounds for making this particular Israelite the hero of a spirited Dunciad. I can almost predict his line of attack. He will call me superficial, crude, barbaric in thought, imperfect in education, offensively arrogant & bigoted, filled with venomous prejudice, wanting in good taste, &c. &c. &c. (LRK 19)
Lovecraft did write this poem, but refrained from publishing it. Conversely, HPL delighted in making a Jewish friend in the form of Samuel Loveman, a poet and bookman who was drawn in to amateur journalism, and to Lovecraft was the picture of "assimilation"—a popular concept at the time where it was expected that immigrants would adapt to American life, learning English and adapting American manners, etc. Another such "assimilated" individual that Lovecraft met at the time was Sonia Haft Greene - a Russian emigre of Jewish heritage.
Through her invitation, Lovecraft first visited New York; and in her memoir she spoke of the lead-up to their marriage:
Long before H. P. and I were married he said to me in a letter when speaking of Loveman, “Loveman is a poet and a literary genius. [...] The only discrepancy I find in him is that he is of the Semitic race, a Jew.”
Then I replied that I was a little surprised at H. P.’s discrimination in this instance—that I thought H. P. to be above such a petty fallacy—and that perhaps our friendship might find itself on the rocks under the circumstances, since I too am of the Hebrew people—but that surely, he, H. P., could not have been serious, that elegance of manner, cultural background, social experience and the truly artistic temperament, intellectuality and refinement surely do not choose any particular color, race or creed; that these attributes should be highly appreciated no matter where they may be found!
It was only after several such exchanges of letters that he put the “pianissimo” on his thoughts (perhaps) and curtailed his outbursts of discrimination. In fact, it was after this that our own correspondence became more frequent and more intimate until, as I then believed, H. P. became entirely rid of his prejudices in this direction, and that no more need have been said about them. (Davis 26)
It was his prejudice against minorities, especially Jews, that prompted me to invite H. P. and S. L. to spend some time in New York, so that if H. P. never met a Jew before, I was happy to know that for the first time he would meet two of them, both of whom were favorably cultured and enlightened, and that the favored of the race is not limited to this infinitesimal number. Unfortunately, one often judges a whole people by the character of the first ones he meets. (Davis 26)
Lovecraft's first taste of New York did nothing to cure him of his prejudices; and their sudden marriage in 1923 saw him move out of home for the first time. The couple struggled with financial and health difficulties—Sonia lost her job, Lovecraft couldn't land or hold one; she ended up in the hospital, and finally had to take a job out west...and New York began to wane on HPL. Sonia commented in her memoir:
He admired the anciency and quaintness of that part of Brooklyn; but when he saw the crowds in the subway, on the streets, and in the parks, he actually hated them and suffered through that hate. He referred chiefly to Semitic peoples. These he called “beady-eyed, rat-faced Asiatics”. And all foreigners in general were “mongrels and outsiders”. (Davis 12)
H. P. Lovecraft never uses this exact language in his letters, although it comes close to some of his descriptions. The marriage would, ultimately, end in failure: HPL couldn't afford to live in New York, and went back to Providence to move in with an aunt. Sonia did not wish to live apart, but neither would the aunts tolerate her to be seen supporting her husband—genteel poverty was tolerable for them, but the loss of social status was apparently not. So she filed for divorce. Lovecraft would later state that the reasons for the failure of his marriage were primarily financial...but it's certain that his prejudices, still extant at that point and maybe heightened by the stresses of failing to get by in a strange, cosmopolitan city, probably didn't help.
Lovecraft's return to Providence marked the start of his most productive period of writing fiction, mostly for Weird Tales, and his famous correspondence with other writers—several of whom, like Robert Bloch, Julius Schwartz, and Kenneth Sterling turned out to be Jewish; Lovecraft was at pains to avoid offending these folks in his letters, and Samuel Loveman was actually surprised after Lovecraft's death to find out something of Lovecraft's thoughts on Jews and Hitler during the later 1930s.
Not to dissuade other answers, but u/ancienthistory addressed something similar to this in It's often remarked that author H.P. Lovecraft was incredibly racist even for his time, just how racist was he in comparison to his contemporaries?